Avian Reproduction Research Articles

Avian Reproduction in a Warming World

Weather influences both the distribution and life-history strategies of birds. Temperature ranks amongst the more important weather parameters in this regard since warming springs in temperate and high latitudes and more frequent heat-waves globally have caused major changes in breeding phenology and negatively affected adult and juvenile survival, respectively. Both long-term and stochastic changes in temperature can have fundamental consequences for avian reproduction even when the effects are not lethal, such as via thermal constraints on parental provisioning and chick growth. To date, most of what we know about temperature effects on nestling development and parental effort during reproduction is based on correlative data. In addition, an increasing amount of evidence indicates that temperature change also significantly affects birds that breed in cooler temperate areas, which so far has been somewhat overlooked. Therefore, in this perspective piece, we outline the existing literature on temperature effects on nestling development and parental behavior, with an emphasis on what needs to be done to address the causal effects of temperature change on avian reproduction under climate change. We finish by providing an outlook over future avenues of research, and give suggestions of some specific areas that might be especially promising in developing this field of research. (Less)

Autoclaving Nest-Material Remains Influences the Probability of Ectoparasitism of Nestling Hoopoes (Upupa epops).

Simple SummaryMicroorganisms may have direct negative effects on their animal hosts and cause diseases, but some others provide animals with protection against infections, parasites, and even predators. However, parasites or predators might take their cue from odors produced by bacteria, even those from protecting microorganisms, which could turn net benefits of bacteria that are a priori considered beneficial into a neutral or even negative outcome. This possibility has scarcely been studied in wildlife populations; we manipulated the bacterial community of nest-material of hoopoes and detected a negative effect in terms of the intensity of parasitism by blood-sucking flies that nestlings suffer. We also detected a positive link between the bacterial density of the nest-materials and the intensity of ectoparasitism, which further points at the importance of the bacteria determining the level of parasitism. Blood-sucking ectoparasites are also disease vectors, affecting both humans and livestock, and considering the role of the bacterial environment might help to establish new transmission control protocols.Nest bacterial environment influences avian reproduction directly because it might include pathogenic- or antibiotic-producing bacteria or indirectly because predators or ectoparasites can use volatile compounds from nest bacterial metabolism to detect nests of their avian hosts. Hoopoes (Upupa epops) do not build nests. They rather reuse holes or nest-boxes that contain remains of nest-materials from previous breeding seasons. Interestingly, it has been recently described that the nest’s bacterial environment partly affects the uropygial gland microbiota of hoopoe females and eggshells. Blood-sucking ectoparasites use chemical cues to find host nests, so we experimentally tested the hypothetical effects of microorganisms inhabiting nest-material remains before reproduction regarding the intensity of ectoparasitism suffered by 8-day-old nestling hoopoes. In accordance with the hypothesis, nestlings hatched in nest-boxes with autoclaved nest-material remains from the previous reproductive seasons suffered less from ectoparasites than those hatched in the control nest-boxes with nonautoclaved nest-material. Moreover, we found a positive association between the bacterial density of nest-material during the nestling phase and ectoparasitism intensity that was only apparent in nest-boxes with autoclaved nest-material. However, contrary to our expectations, nest bacterial load was positively associated with fledgling success. These results suggest a link between the community of microorganisms of nest-material remains and the intensity of ectoparasitism, and, on the other hand, that the nest bacterial environment during reproduction is related to fledging success. Here, we discuss possible mechanisms explaining the experimental and correlative results, including the possibility that the experimental autoclaving of nest material affected the microbiota of females and nestlings’ secretion and/or nest volatiles that attracted ectoparasites, therefore indirectly affecting both the nest bacterial environment at the nestling stage and fledging success.

C1EIP Functions as an Activator of ENO1 to Promote Chicken PGCs Formation via Inhibition of the Notch Signaling Pathway.

The production of germ cells, especially primordial germ cells (PGCs), is important for avian stem cells and reproduction biology. However, key factors involved in the regulation of PGCs remain unknown. Here, we report a PGC-related marker gene: C1EIP (Chromosome 1 Expression in PGCs), whose activation and expression are regulated by the transcription factor STAT3 (signal transducer and activator of transcription 3), histone acetylation, and promoter methylation. C1EIP regulates PGCs formation by mediating the expression of PGC-associated genes, such as CVH (Chicken Vasa Homologous) and CKIT (Chicken KIT proto-oncogene). C1EIP knockdown during embryonic development reduces PGC generation efficiency both in vitro and in ovo. Conversely, C1EIP overexpression increases the formation efficiency of PGCs. C1EIP encodes a cytoplasmic protein that interacts with ENO1 (Enolase 1) in the cytoplasm, inhibits the Notch signaling pathway, and positively regulates PGC generation. Collectively, our findings demonstrate C1EIP as a novel gene involved in PGC formation, which regulates genes involved in embryonic stem cell differentiation through interaction with ENO1 and subsequent inhibition of the Notch signaling pathway by the impression of Myc (MYC proto-oncogene).

Providing urban birds nutritious food to feed chicks reduces urban versus rural breeding success disparities.

In Focus: Seress, G, Sándor, K, Evans, KL, Liker, A. (2020) Food availability limits avian reproduction in the city: An experimental study on great tits Parus major . Journal of Animal Ecology. 89. Animals in urban areas face a multitude of stressors, but how each stressor impacts survival and fitness can be difficult to disentangle. We need experimental manipulations of suspected stressors to examine causal relationships with traits of free-living urban and rural animals. In this issue, Seress and colleagues take on an intensive experimental approach to test whether one potential stressor-limited natural food sources in cities-can explain reduced avian reproductive success in urban areas. They employ a full factorial design, including both food supplemented and control broods in both urban and forest great tit Parus major populations. The findings are clear. Reduced food availability is the key factor limiting urban offspring growth and survival, at least in this well-studied species. Indeed, the extra insects fed to urban chicks greatly reduced the significant differences in survival rates and body sizes between urban and forest broods. The findings are also sobering. Urban insect populations would need to more than double to erase differences in reproductive success between urban and rural bird populations, an unlikely outcome with the ever-increasing urbanization of habitats.

Reproduction in the Eared Dove: An exception to the classic model of seasonal reproduction in birds?

In avian species living at high altitudes and latitudes, reproductive events are largely controlled by photoperiod, with changes being perceived mainly through encephalic photoreceptors located in the hypothalamus. It is known that during long day periods (reproductive periods), the information transmitted by brain photoreceptors triggers the production of thyroid hormones that regulate GnRH secretion, inducing secretion of pituitary gonadotropins. As a result, gonads develop and grow and the production of gonadal sex hormones, testosterone and estradiol increases (classic gonadal cycle). During short day periods (non-reproductive periods) on the other hand, the gonads regress, and plasma gonadal steroid levels are low. By means of this mechanism, birds synchronize their physiology and reproductive behaviors with seasonal changes in the environment. However, it appears that not all avian species comply with this general reproductive pattern. For example, the Eared Dove (Zenaida auriculata), a South American opportunistic breeding columbiform, has been reported to successfully reproduce throughout the year, making it an interesting avian system for studying the endocrine basis of avian reproduction. In view of a clear lack of seasonal variability in testicular weight and size (the classic gonadal regression/recrudescence cycle) in the male Eared Dove, we examined whether their reproductive aseasonality could be the result of being in a continuous state of reproductive preparedness. Our results show that despite the absence of a marked gonadal cycle in terms of gonadal volume, plasma testosterone levels in males were minimal during autumn-winter, reaching maximum values during spring-summer. This indicates that male gonad function is not seasonal in terms of spermatogenesis but that circulating testosterone levels are correlated with photoperiod, demonstrating an exception to the classic model of reproduction in birds.

NOTES ON THE BREEDING BIOLOGY OF THE TUMBESIAN AVIFAUNA IN SOUTHWEST ECUADOR AND NORTHWEST PERU

This paper contributes to the growing body of literature on the reproductive biology of South American birds by providing 823 records of reproduction for 197 species breeding within the Tumbesian biome of Peru and Ecuador. Where applicable, we include notes on adult behaviour, nest architecture, eggs, nestlings, and fledglings. In general, our observations support previous reports of the seasonal nature of avian reproduction in the region.

Non‐photic environmental cues and avian reproduction in an era of global change

Ultimate factors such as food availability and weather create optimal windows of time for birds to reproduce. However, within a given year, birds must rely upon proximate environmental information such as photoperiod, food, temperature, social cues and other factors to anticipate when that window will occur and prepare physiologically for breeding. While avian responses to photoperiod are relatively well understood, less is known about how birds use non‐photoperiodic information in reproductive timing decisions – even though understanding how birds use non‐photic cues is an important component of predicting their responses to global change. We review research on the regulation of reproductive physiology and clutch initiation by non‐photic cues within and across avian species. We evaluate hypotheses in the literature about the integration of photoperiodic and non‐photic cues in reproductive timing and about differences in non‐photic cue‐use between the sexes and across species. We show how regulation of reproduction by non‐photic cues may influence species’ responses to climate change and highlight research opportunities moving forward.

The value of avian gross pathology in identifying endocrine disrupting properties

The European Chemical Agency and European Food Safety Authority recommend that gross pathology findings, from avian reproduction studies, be used to support assessment of potential endocrine disrupting properties of active pesticidal and biocidal substances. In open literature, little information is available on the utility of gross pathology data for informing endocrine evaluations. Here the gross pathology data from historical control groups of 51 northern bobwhite and 51 mallard reproduction tests is analyzed to evaluate the utility of such information. Incidence of gross morphology findings in untreated birds may aid the interpretation of some gross abnormalities, potentially indicative of an endocrine interaction (e.g. reproductive condition). Statistical analysis of the historical control data indicates that gross pathology is not likely to be useful for detecting endocrine effects as abnormalities with relatively high increases in prevalence (more than 20–30%, depending on prevalence in controls) are reliably interpreted as a treatment response. Gross pathology changes are only indicative and not diagnostic of endocrine interactions making it difficult to distinguish gross pathology abnormalities, due to endocrine-mediated effects, from systemic toxicity. This work demonstrates the utility of using historical control analyses to establish the value and properties of selected endpoints for regulatory applications.

Identification of single nucleotide polimorphisms and restriction enzym on prolactin gene in Alabio and Mojosari duck

Prolactin plays important roles in avian reproduction as it induces broody behavior and regulates follicular development. The objectives of this study were to detect Single Nucleotide Polymorphisms (SNPs) of prolactin gene in Alabio and Mojosari ducks and determine the restriction enzymes for genotyping. Genomic DNA was isolated from 50 blood samples per each Alabio and Mojosari ducks. PCR amplification and sequencing were carried out to identify the SNP. In this study, SNP T-6068C was found based on three GenBank sequences alignment. Two SNPs (C-5796A and T-5817C) in intron 4 region were detected based on sequences of Alabio and Mojosari PCR products. Enzymes Fok1, BtsCI, BsrI were detected to recognize the SNP C-5796A. SNP T-6068C can be digested by enzym TspDTI. However no enzym was detected to recognize SNP T-5817C. In conclusion the SNPs detected from this study may be used in future studies to investigate the association of prolactin gene and egg production traits in Alabio and Mojosari ducks.

Construction materials affect the hydrological properties of bird nests

AbstractBird nests are highly variable structures that represent extended phenotypes, which may have a range of roles during avian reproduction, but all nests serve as the location for incubation of eggs. Nest characteristics should counter any adverse weather conditions that could potentially reduce hatchability or chick survival. Thermal properties of nests are relatively well studied, but the effects of moisture on nest insulation are largely unknown. Wet nests could reduce thermal insulation or deleteriously cool the eggs or nestlings. In this study, a novel method of simulated rainfall was applied to open‐cup nests from nineteen different passerine species. The amount of water absorbed by the nest and the time it took to dry were recorded. To determine the factors affecting these characteristics, nests were deconstructed to provide data on materials used. Compared with smaller nests, larger nests absorbed more water and took longer to dry. The amount of water absorbed was a function of the proportion of grass, moss, roots and hair present in the nest. The time taken for the nest to dry completely was affected by the proportion of grass, moss, and hair in the nest. When tested individually, the materials all had different rates of water absorption and took different times to dry; moss absorbed the most water and took the longest time to dry. We concluded that simulated rainfall was a realistic approach to understanding the hydrological characteristics of nests. Structural considerations for nest construction may affect the hydrological properties of nests, but ex situ studies provide no information about the possible shelter provided to a nest by its immediate surroundings. Further research into nest function should consider the importance of exposure to water to nest construction and function.

Mercury Exposure and Altered Parental Nesting Behavior in a Wild Songbird.

Methylmercury is a neurotoxin and endocrine disruptor and may impair avian reproduction directly through embryotoxicity or by altering parental care behaviors. We studied mercury exposure and incubation behavior of free-living tree swallows ( Tachycineta bicolor) nesting in artificial nest boxes. Using small temperature dataloggers, we measured incubation constancy (the proportion of each day the female spent incubating eggs), the number of incubation recesses taken per day, and the duration of incubation recesses. We also assessed maternal mercury exposure by measuring mercury concentrations in both blood and eggs. Females with higher mercury concentrations exhibited lower incubation constancy, took more frequent and shorter incubation recesses, and were more likely to take incubation recesses that caused nest temperature decreases that were likely to slow embryonic development. Overall, females that laid eggs with the highest observed mercury concentration (0.53 μg/g fww) spent an average of 12% less time incubating their eggs over the 14-day incubation period than females that laid eggs with the lowest mercury concentration (0.07 μg/g fww). Because less time spent incubating can lower egg temperatures, slow embryonic development, and potentially lengthen the incubation period, these results suggest that environmentally relevant mercury concentrations may negatively influence reproduction by altering parental nesting behaviors of wild songbirds.

Is plastic ingestion in birds as toxic as we think? Insights from a plastic feeding experiment

Plastic pollution is a modern tragedy of the commons, with hundreds of species affected by society's waste. Birds in particular mistake plastic for prey, and millions of wild birds carry small plastic loads in their stomach and are exposed to potential toxicological effects. It is currently unknown how severely the toxicological and endocrine disrupting chemicals in plastic affect avian development, reproduction and endocrine function. To address this question, we conducted multi-generational plastic feeding experiments to test the toxicological consequences of plastic ingestion at environmentally relevant loads in Japanese quail, Coturnix japonica, investigating parental and two filial generations. Contrary to expectations, we found no evidence of lasting toxicological effects on mortality, adult body weight, organ histology, hormone levels, fertility, hatch rates and eggshell strength in birds experimentally fed plastic. However, we found plastic ingestion causes higher frequencies of male reproductive cysts and minor delays in chick growth and sexual maturity, though without affecting ultimate survival or reproductive output. We report that although plastic ingestion causes detectable endocrine effects in our model species, our lack of finding mortality, morbidity and adverse reproductive outcomes may challenge the common hypothesis of severe toxicological harm and population-level effects when environmentally relevant loads of plastic are ingested.

Element Concentrations in Tree Swallows (Tachycineta bicolor) from the U.S. and Binational Great Lakes Areas of Concern.

Selected elements were targeted in state Remedial Action Plans as one group of chemicals affecting the Beneficial Use Impairments of Great Lakes Areas of Concern (AOCs). Livers of nestling tree swallows, Tachycineta bicolor, were harvested from 76 sites in the Great Lakes, which included multiple sites at 27 AOCs and 12 reference sites from 2010 to 2015, and were analyzed for 21 elements. Mercury concentrations were at background levels at all sites. Elevated cadmium (Cd) concentrations were associated with industry. The highest Cd values were from the Black River, OH AOC and were associated with historic coke production but were not at toxic levels. Lead (Pb) concentrations were highest on the Rouge River, MI AOC-the oldest and most heavily populated and industrialized area in southeast Michigan. Individual Pb concentrations were elevated to a level associated with delta-aminolaevulinic acid dehydratase inhibition but not to a level considered toxic. In contrast, livers harvested from sites on the southwest shore of Lake Michigan had selenium (Se) concentrations elevated to levels associated with reduced avian reproduction. One likely source of the high Se concentrations was pollution from a local coal-fired power plant. Concentrations of the remaining elements were at background levels.

互花米草入侵对鸟类的生态影响

PDF HTML阅读 XML下载 导出引用 引用提醒 互花米草入侵对鸟类的生态影响 DOI: 10.5846/stxb201801110089 作者: 作者单位: 南京林业大学生物与环境学院,南京林业大学生物与环境学院,南京林业大学生物与环境学院,南京林业大学生物与环境学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（31670432）；国家重点研发计划（2016YFC0502704） Ecological effects of invasion by the smooth cordgrass Spartina alterniflora on birds Author: Affiliation: College of Biology and the Environment,Nanjing Foresty University,College of Biology and the Environment,Nanjing Foresty University,College of Biology and the Environment,Nanjing Foresty University,College of Biology and the Environment,Nanjing Foresty University Fund Project: The National Natural Science Foundation of China，The National Major Research Program of China 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:生物入侵威胁本地物种生存，破坏生态系统的结构和功能，是导致全球生物多样性丧失的重要原因之一。外来植物是入侵生物中的重要一类，可以显著改变本地植被群落，并影响其他生物类群。鸟类作为生态系统中的较高营养级，对由入侵植物引起的栖息地变化十分敏感。互花米草自引入中国沿海以来，其分布区域不断扩散，多数研究认为互花米草入侵造成本地生物多样性降低和生态系统退化。系统梳理了互花米草入侵对鸟类栖息地、食物资源、繁殖、群落等方面的生态影响。主要负面影响有：（1）植被群落结构不利于鸟类栖息、筑巢、觅食；（2）鸟类食物资源丰度和多样性下降；（3）本地鸟类种群数量和物种多样性显著下降。在我国东部沿海湿地，互花米草入侵已经显著改变了植被与鸟类分布格局。但随着入侵历史的增长，少数小型雀形目鸟类却可以逐渐适应互花米草生境。互花米草入侵为某些非本地鸟类提供了空白生态位，在一定程度上丰富了本地物种多样性，对互花米草的快速清除反而可能不利于已适应并依赖互花米草生境的鸟类。综上，认为互花米草入侵对鸟类群落甚至整个生态系统的影响可能需要更多研究进行综合评价，应开展长期、大尺度、多因子的监测研究和多物种比较研究，建立生态评价模型并制定科学有效的互花米草管理对策。 Abstract:As one of the leading causes of the loss of global biodiversity, biological invasion severely threatens the existence of native species and destroys the structure and function of the original ecosystem. Alien plants,an important category of invasive species, can significantly change the local vegetation communities, and have a major effect on other related biological groups. Birds, which are positioned at the higher trophic levels in ecosystems, are particularly sensitive to changes in habitats caused by invasive plants. The typical smooth cordgrass (Spartina alterniflora) continued to spread since it was introduced to China's coastal regions, which provided the impression that the smooth cordgrass might decrease biodiversity and degenerate the ecosystem. In this study, we systematically elaborated the ecological effects of the invasive smooth cordgrass on avian habitats, food resources, reproduction, and communities. The negative effects of the invasion mainly included:(1) the unsuitability of the altered vegetation community structure for avian roosting, nesting, and foraging; (2) the decrease in richness and diversity of avian food resources; (3) the remarkable decline in the number of populations and species diversity of native birds. The invasion of smooth cordgrass in China's eastern coastal wetlands had changed the distribution pattern of native vegetation and birds drastically. However, some small passerines could adapt to the habitat of long time invasion by the smooth cordgrass gradually. Indeed, several non-native birds have adapted to the newly formed ecological environment, which provided free ecological niches for them, and consequently enriched the diversity of native species in some extent. Therefore,the rapid weeding of smooth cordgrass might be detrimental to those birds, which have already adapted to the smooth cordgrass and become dependent on it. In summary,further research focusing on long-term, large-scale, and multifactorial monitoring, and multi-species comparisons, are necessary for comprehensively evaluating the effect of invading smooth cordgrass on the avian community and the entire ecosystem, with the aim of establishing ecological evaluation models and adopting scientific and efficient management countermeasures against the invasion. 参考文献 相似文献 引证文献

Stream type influences food abundance and reproductive performance of a stream specialist: the Brown Dipper (Cinclus pallasii)

Avian reproduction and population growth are highly dependent on food availability. Consequently, studies on these variables require accurate estimates of food abundance that may vary in space and time. Dippers (Cinclus spp.) are obligate stream predators in freshwater ecosystems. Although it is well known that dippers are affected by aquatic macroinvertebrate density and proportion of riffle habitat, rarely are these two factors combined to estimate their food availability. We developed a new method to estimate food availability and tested the relationship of food availability with reproduction performance of the Brown Dipper (Cinclus pallasii) in Taiwan from 2013 to 2015. We defined three stream types (stony riffles, sandy runs, and pools) with water depth and benthic substrate. Macroinvertebrate biomass was significantly greater in stony riffles than in sandy runs. We then measured the area of the three stream types in a 400-m stream segment centering on each Brown Dipper’s nest. The area of stony riffles was multiplied by average macroinvertebrate density of each stream to represent food availability in stony riffles of each territory. Response variables on reproductive performance (e.g., laying date, clutch size, fledgling number, and territory length) of each nest were recorded. Linear mixed-effects models showed that food availability estimated using the area of stony riffles was significant correlated with all aspects of reproductive performance of Brown Dippers and was a better predictor than food availability estimated in the total water area. This study also demonstrated that summer floods and winter flows (high or low water level) could influence food availability in the dipper’s breeding season by different mechanisms.

Organochlorines, perfluoroalkyl substances, mercury, and egg incubation temperature in an Arctic seabird: Insights from data loggers.

In birds, incubation-related behaviors and brood patch formation are influenced by hormonal regulation such as prolactin secretion. Brood patch provides efficient heat transfer between the incubating parent and the developing embryo in the egg. Importantly, several environmental contaminants are already known to have adverse effects on avian reproduction. However, relatively little is known about the effect of contaminants on incubation temperature (Tinc ) in wild birds. By using temperature thermistors placed into artificial eggs, we investigated whether the most contaminated parent birds are less able to provide appropriate egg warming and thus less committed to incubating their clutch. Specifically, we investigated the relationships among 3 groups of contaminants (organochlorines, perfluoroalkyl substances [PFASs], and mercury [Hg]) with Tinc and also with prolactin concentrations and brood patch size in incubating Arctic black-legged kittiwakes (Rissa tridactyla). Our results reveal that among the organochlorines considered, only blood levels of oxychlordane, the main metabolite of chlordane, a banned pesticide, were negatively related to the minimum incubation temperature in male kittiwakes. Levels of PFASs and Hg were unrelated to Tinc in kittiwakes. Moreover, our study suggests a possible underlying mechanism: since we reported a significant and negative association between blood oxychlordane concentrations and the size of the brood patch in males. Finally, this reduced Tinc in the most oxychlordane-contaminated kittiwakes was associated with a lower egg hatching probability. Environ Toxicol Chem 2018;37:2881-2894. © 2018 SETAC.

Effects of drought on brood parasite body condition, follicle development, and parasitism: Implications for host–parasite dynamics

Temporal variation in avian brood parasite condition and reproduction seem to affect host–parasite dynamics. Few studies, however, consider dynamics from the perspective of the parasite. Here we examined how brood parasite body condition and reproductive output vary both seasonally and annually and investigate the resultant impacts on nest parasitism rates of a host species. In the breeding seasons of 2011 and 2012, we collected female Brown-headed Cowbirds (Molothrus ater) from Fort Hood, Texas, and conducted morphometric, phenotypic, and physiological measurements on carcasses. During the same period, we also monitored nests of Black-capped Vireos (Vireo atricapilla) and recorded parasitism occurrence. Based on an analysis of >400 cowbirds, we found that cowbird body condition was significantly lower in 2012 than in 2011. Fewer females developed follicles in 2012 and follicle development was substantially delayed. Further, nest parasitism rates were significantly lower in 2012 and vireo nest success was significantly higher. The substantial variation we observed in cowbird body condition, follicle development, and parasitism may be related to a record-breaking drought that occurred in 2011. Cowbirds appeared to suffer negative carryover effects from the drought, likely due to reduced food resources, although similar effects on vireos were not observed. Detrimental effects of drought on cowbirds but not on vireos may have significant implications for host–parasite dynamics under changing climate conditions.

Mercury and lead exposure in avian scavengers from the Pacific Northwest suggest risks to California condors: Implications for reintroduction and recovery

Mercury (Hg) and lead (Pb) are widespread contaminants that pose risks to avian scavengers. In fact, Pb exposure is the primary factor limiting population recovery in the endangered California condor (Gymnogyps californianus) and Hg can impair avian reproduction at environmentally relevant exposures. The Pacific Northwest region of the US was historically part of the condor's native range, and efforts are underway to expand recovery into this area. To identify potential threats to reintroduced condors we assessed foraging habitats, Hg and Pb exposure, and physiological responses in two surrogate avian scavenger species (common ravens [Corvus corax] and turkey vultures [Cathartes aura] across the region between 2012 and 2016. Mercury exposure near the Pacific coast was 17–27-fold higher than in inland areas, and stable carbon and sulfur isotopes ratios indicated that coastal scavengers were highly reliant on marine prey. In contrast, Pb concentrations were uniformly elevated across the region, with 18% of the birds exposed to subclinical poisoning levels. Elevated Pb concentrations were associated with lower delta-aminolevulinic acid dehydratase (δ-ALAD) activity, and in ravens there was an interactive effect between Hg and Pb on fecal corticosterone concentrations. This interaction indicated that the effects of Hg and Pb exposure on the stress axis are bidirectional, and depend on the magnitude of simultaneous exposure to the other contaminant. Our results suggest that condors released to the Pacific Northwest may be exposed to both elevated Hg and Pb, posing challenges to management of future condor populations in the Pacific Northwest. Developing a robust monitoring program for reintroduced condors and surrogate scavengers will help both better understand the drivers of exposure and predict the likelihood of impaired health. These findings provide a strong foundation for such an effort, providing resource managers with valuable information to help mitigate potential risks.

Best Paper Award.

Best Paper Award.

Grazing pressure affects offspring sex ratio in a socially monogamous passerine on the Tibet Plateau

Livestock grazing can affect habitat structure and availability of arthropod prey for grassland birds, and ultimately determines habitat quality. The habitat quality may affect breeding strategies (e.g. sex ratio adjustment) in bird species, but studies investigating grazing intensity on offspring sex ratio are still rare. In this paper, we examined the effect of grazing intensity by livestock on the secondary sex ratio of an alpine‐steppe passerine, the isabelline wheatear Oenanthe isabellina, on the Tibet Plateau. Offspring sex ratio of isabelline wheatears significantly correlated with a quadratic term – (grazing intensity)2. The wheatears nesting in areas grazed at low intensity by mixed livestocks produced significantly more sons than those in ungrazed area (0.41 vs 0.58, Z = –2.836, p = 0.005), while brood sex ratios from other treatments (ungrazing vs intensive grazing and low‐intensity grazing vs intensive grazing) did not differ significantly. Variation in offspring sex ratio was not related to other factors such as maternal condition, paternal condition and other two‐way interactions. These results suggest that breeding birds of grasslands are sensitive to variation in habitat conditions, and provide additional evidence that grazing intensity affects avian reproduction in cryptic ways that are rarely studied. Our findings suggest that flexible management including timely rotational grazing is needed to optimize bird species reproduction and maintain ecosystem health.